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- Add slowly with cooling and shaking 10cm3 of
concentrated sulphuric acid.
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- Ensure that the mixture is homogeneous, then fit the flask
with a reflux water-condenser and boil the mixture gently for
10 minutes. Rearrange the position of the condenser for
distillation, and distil off about two-thirds of the mixture.
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- Why must the mixture be homogeneous?
- Concentrated sulphuric acid is much denser than any of the
other reagents. If not well mixed initially, the solution is liable to get
too hot and boil uncontrollably when mixing occurs later in the
reaction.
- What
is a reflux water-condenser?
- A reflux water condenser is a Liebig condenser arranged
vertically above the reaction flask; vapors are condensed and returned to
the flask, the contents of which can therefore be boiled for long periods
without any loss of material.
- Why is
the reaction comparatively slow?
- Most organic reactions are slow since they involve the
breaking of strong covalent bonds. The proportion of molecular collisions
that have the necessary activation energy is usually fairly low.
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- Transfer the
distillate to a separating funnel and add about 25 cm3 of 30%
sodium carbonate solution. Stopper the funnel, invert it, and
shake, opening the tap from time to time.
- Allow the two
layers to separate and carefully run off and reject the lower layer,
ensuring that the sodium carbonate is removed as completely as possible.
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- What is the function of the sodium carbonate solution?
- The distillate contains traces of ethanoic acid and
perhaps some sulphuric acid. Sodium carbonate solution removes this.
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Why
do you need to open the tap from time to time?
- The neutralisation with sodium carbonate produces carbon
dioxide gas; opening the tap releases this and avoids a build-up of
pressure that might blow the stopper out of the funnel.
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- Prepare a solution of 25g of calcium chloride in 25 cm3
of water, add it to the crude ethyl ethanoate in the funnel, and
shake vigorously. Allow the mixture to separate, and run off the lower
aqueous layer as completely as possible.
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- What
is the function of the calcium chloride at this stage of the
preparation?
- The crude ethyl ethanoate contains traces of ethanol; the calcium
chloride solution removes this since it complexes with the ethanol
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- Run the ethyl ethanoate into a small conical flask, add a few lumps
of granular anhydrous calcium chloride, and shake occasionally
until the liquid is clear.
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- What
is the function of the calcium chloride at this stage of the
preparation?
- The solid calcium chloride is a dehydrating agent; it
removes any remaining traces of water from the product.
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- Then decant the liquid into a clean, dry 100 cm3
round-bottom flask, add some anti-bumping granules, and arrange
for distillation including a 0-100oC thermometer in the
apparatus. The distilling flask should be placed in a cold water bath,
which is gradually heated. The ether that is always formed in
this reaction will distil off at 35-40oC, and may be
discarded. Continue to heat, and collect the fraction that boils between
74o and 79oC.
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